1. Field of the Invention
The present invention relates generally to pickup devices for optical disks that are used in conjunction with optical storage and reproduction apparatuses, and in particular to an improvement in a lens supporting structure thereof.
2. Conventional Art
Conventionally, pickup devices for optical disks (referred to as xe2x80x9cpickup devicesxe2x80x9d hereinafter) are typically driven electromagnetically, as shown in FIGS. 7 and 8. In FIGS. 7 and 8, an arrow X indicates a disk tangent direction, i.e., a direction of a tangent to a track at a recording or reproducing position of an optical disk (referred to as xe2x80x9cthe X directionxe2x80x9d hereinafter). Arrows Y and Z indicate a focusing direction perpendicular to a surface of an optical disk on which data is recorded or reproduced (referred to as xe2x80x9cthe Y directionxe2x80x9d hereinafter) and a tracking direction (referred to as xe2x80x9cthe Z directionxe2x80x9d hereinafter), respectively.
The electromagnetically driven pickup device includes a lens holder 4 for holding an objective lens 1. Lens holder 4 has opposite side surfaces perpendicular to the X direction, each with a focusing coil 2 and a tracking coil 3 attached thereto. Opposite to focusing and tracking coils 2 and 3, magnetic-flux generation means corresponding to a magnet 5 is provided, with a magnetic gap 6 therebetween. A U-letter yoke 7 holding magnet 5 and a shielding plate 8 together form a magnetic circuit.
The pickup device also includes a base 9 with various parts positioned and arranged thereon. Base 9 has in the X direction one end with a stand 10 attached thereto. Between side surfaces of stand 10 perpendicular to the X direction and those of lens holder 4 perpendicular to the X direction, two pairs of two spring wires for a total of spring wires 11a-11d supporting lens holder 4 displaceably in the Y and Z directions are provided parallel to each other. Spring wires 11a-11d are rectangular in cross section and each have ends soldered, one to stand 10 and the other to a printed circuit board 12 mounted to lens holder 4.
More specifically, spring wires 11a-11d are processed to have a cross section to obtain a resonant frequency required for displacing lens holder 4 in the Y and Z directions. Furthermore, spring wires 11a-11d each have in the longitudinal direction thereof at a position other than its ends a bent portion 13 functioning as a vibration damping portion (a so-called damping portion), with a Visco Elastic Material (VEM) sheet 14 attached for providing an additional vibration damping property. xe2x80x9cVEMxe2x80x9d is a brand name of a product of 3M Company.
In accordance with the above description, spring wires 11a-11d provided between the side surfaces of stand 10 on base 9 and those of lens holder 4 each have a rectangular cross section, i.e., a cross section allowing a spring constant in the focusing or Y direction and that in the tracking or Z direction to vary from each other. However, spring wires 11a-11d are not limited to such cross section and there is also a pickup device with spring wires 11a-11d each having a round cross section. Such spring wires 11a-11d round in cross section have the same spring constant in the both Y and Z directions. Thus, a resonant frequency required for displacing lens holder 4 in the Y direction is equal to that required for displacing lens holder 4 in the Z direction.
The above conventional pickup device has such an inconvenience as described below: since spring wires 11a-11d rectangular in cross section are formed by etching, punching or the like, using as much as such four spring wires 11a-11d would inevitably result in an increased cost. Furthermore, forming bent portion 13 in each of four spring wires 11a-11d and attaching VEM sheet 14 to each of four spring wires 11a-11d are time-consuming in processing and assembling spring wires 11a-11d resulting in a further increased cost.
Furthermore, with spring wires 11a-11d each having bent portion 13, lens holder 4 tends to incline when it is displaced in the Y direction. Furthermore, in soldering spring wires 11a-11d to lens holder 4 and stand 10, spring wires 11a-11d, rectangular in cross section, must have their sides positioned parallel to the Y and Z directions, respectively. In doing so, it is difficult to avoid some error introduced when the wires are assembled, and such assembling error tends to result in a vibration which can in turn cause an inclination of lens holder 4, a signal degradation and the like. Furthermore, while for an optical recording medium of high density a lens with large numerical aperture is preferably used to improve signal quality, as a lens""s numerical aperture is increased even a slight inclination of lens holder 4 would result in a large coma-aberration and thus increase a jitter which can degrade signal quality.
In contrast, if spring wires 11a-11d are round in cross section, their assembling errors can readily be controlled and lens holder 4 thus hardly inclines. However, spring wires 11a-11d round in cross section cannot have a spring constant in the Y direction and that in the Z direction that vary from each other. Thus it is difficult to provide a resonant frequency optimized for each direction. This would result in a limitation in miniaturizing the general configuration and reducing power consumption.
Furthermore, although not shown, the conventional pickup device has an objective lens and a magnetic head arranged opposite to each other with a recording disk posed therebetween. This requires that a beam directed from an actuator and a magnetism generating portion of the magnetic head be aligned with each other. As a result, the device""s general configuration is increased in size and its number of parts and cost would be increased. Furthermore, currently it is desired that a magnetic head recording data at high density should have superior high-frequency characteristics and the magnetic head thus should be supplied with current through a conductor line with reduced loss or reduced resistance.
The present invention has been made to solve the conventional disadvantages described above and contemplates a pickup device having a configuration capable of controlling an inclination of a lens holder while ensuring a sufficient displacing property in focusing and tracking directions.
To achieve the above object the pickup device of the present invention in a first aspect includes a lens holder for holding an objective lens, focusing and tracking coils attached on a side surface of the lens holder in a disk tangent direction, a yoke holding a magnetic-flux generation means arranged opposite to the focusing and tracking coils, a spring wire supporting the lens holder displaceably in focusing and tracking directions, and a base with the lens holder and the yoke arranged thereon. This device is characterized in that two sets of more than two spring wires are arranged in parallel, one set for each side of the lens holder perpendicular to the tracking direction, wherein of more than two spring wires of each set, at least one spring wire has a cross section allowing a spring constant in the focusing direction and that in the tracking direction to vary from each other and is also positioned farther or closer than the other spring wires away from or to a centerline passing a center of the objective lens and running in the disk tangent direction.
As such, a total of more than five spring wires supporting the lens holder can provide a sufficiently strong lens-holder supporting structure. Furthermore, at least one of more than two spring wires of each set that has a cross section allowing a spring constant in the focusing direction and that in the tracking direction to vary from each other, allows a resonant frequency optimized for each of the focusing and tracking directions without increasing cost. Furthermore, the spring wire having a cross section allowing a spring constant in the focusing direction and that in the tracking direction to vary from each other, allows a larger spring constant in a direction of the objective lens""s rotation around the centerline running in the disk tangent direction, than a spring wire having the same spring constant in the tracking and focusing directions. As a result, the lens holder can have a reduced inclination around such centerline.
The pickup device of the present invention in a second aspect has a lens holder for holding an objective lens, focusing and tracking coils arranged on a side surface of the lens holder perpendicular to a disk tangent direction, a yoke holding a magnetic-flux generation means arranged opposite to the focusing and tracking coils, a spring wire supporting the lens holder displaceably in focusing and tracking directions, and a base with the lens holder and the yoke arranged thereon. This pickup device is characterized in that two sets of more than two spring wires are provided, one set for each side of the lens holder perpendicular to the tracking direction, wherein of more than two spring wires of each set, at least one spring wire has a cross section allowing a spring constant in the focusing direction and that in the tracking direction to vary from each other and is also inclined in the tracking direction while the remaining spring wires are arranged such that the two sets of spring wires are parallel to each other.
As such, the spring wires having a cross section allowing a spring constant in the focusing direction and that in the tracking direction to vary from each other can provide an optimized resonant frequency without increasing cost and also reduce an inclination of the lens holder that is attributed to the objective lens""s rotation around a centerline running in the disk tangent direction. Furthermore, the spring wires having a cross section allowing a spring constant in the focusing direction and that in the tracking direction to vary from each other and obliquely intersecting both the disk tangent direction and the tracking direction, can save more space and thus miniaturize the pickup device, since if a spring wire is arranged parallel to the disk tangent direction, increasing the wire""s spring constant in a direction of the objective lens""s rotation around the centerline running in the disk tangent direction, requires the spring wire to have a large interval in the focusing direction and/or the tracking direction, whereas if a spring wire obliquely intersects the disk tangent direction, it does not require such a large interval as described above and only requires a relatively small space while it also allows a large spring constant around the centerline running in the disk tangent direction.
In accordance with the present invention in the first and second aspects a pickup devices according to a preferable embodiment includes a vibration damping portion provided to a spring wire having a spring constant in the focusing direction and that in the tracking direction varying from each other. As such, a vibration that can cause an inclination of the lens holder, a signal degradation and the like hardly occurs.
In accordance with the present invention in the first and second aspects a pickup device according to another preferable embodiment includes a spring wire rectangular in cross section, having a spring constant in the focusing direction and that in the tracking direction varying from each other, and the remaining spring wires round in cross section. The spring wires round in cross section and larger in number than that rectangular in cross section can be readily formed and the cost therefor can thus be reduced. Furthermore, such spring wires round in cross section can be readily assembled and their assembling errors can thus be readily controlled.
In accordance with the present invention in the first and second aspects a pickup device according to a still preferable embodiment includes a lens holder holding an objective lens as well as a magnetic head, and more than two spring wires of each set, at least one spring wire used for supplying power to the magnetic head and the remaining wires used for supplying power to the focusing and tracking coils. As such, the objective lens and the magnetic head that are integrated together are situated opposite to an optical recording medium. This can eliminate the necessity of aligning them with each other and thus miniaturize the pickup device.
In accordance with the present invention in the first and second aspects a pickup device according to a still preferable embodiment includes a spring wire feeding power to the magnetic head that is formed of a material having a small electric resistance. As such, power loss and hence power consumption can be advantageously reduced.
As described above, in spite that in the present invention a pickup device uses a total of more than five spring wires of which only at least two spring wires have a cross section allowing a spring constant in the focusing direction and that in the tracking direction to vary from each other, the pickup device can ensure a sufficient displacement of the lens holder in each of the focusing and tracking directions while controlling the lens holder""s inclination and thus provide a resonant frequency optimized without such a cost as otherwise increased as conventional. As such, the focusing and tracking coils displacing the lens holder can effectively consume less power and the coils"" turn counts and the magnet""s size can be effectively optimized, and, with the pickup device having its general configuration miniaturized, power consumption can also be effectively reduced.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.